Hollows and jumps in new slab covering

First of all, hello everyone,

Our bathroom is finally finished with tiles and looks absolutely amazing! We chose tiles in the format 600x600mm with very narrow grout lines. We have a high-quality quick screed underneath and an affordable underfloor heating – which, however, is not intended as heating in the true sense.

So, now we are dealing with the following problem:

Already after the second round of cleaning, we unfortunately had to notice that
1. one of the tiles has a crack! - However, it is hardly visible, actually almost only
detectable by touch. But now we know that this defect is there. The length of the crack is about 15cm. 2. One grout line is cracked. I also noticed by tapping on the tile that it sounds “hollow.”

What do you think, would you immediately complain about this, i.e. inform the company and have it fixed?
I don’t know if it is bad if moisture penetrates there. What I fear, however, is that the tile could break if it is hollow underneath!

Thanks for your tips!
Best regards, Smeralda

Hello Smeralda.
- We also have tiles with heating mats underneath in our bathroom - We know the problem you have very well :)
There can be various reasons for hollow spaces:
1. The fast screed might not have been sufficiently dried! That could also mean that more tiles might come loose in the next few days!
The residual moisture of a subfloor on which tiles are laid should not, to my knowledge, exceed 0.3% (SIA Swiss standard) or 0.5% (DIN German standard). The residual moisture should have been measured with the so-called CM measuring device! Was a measurement carried out? Because residual moisture is a problem not only with parquet but also with tile coverings – with tiles exactly because the moisture cannot escape from the subfloor after laying and therefore can lead to detachments/hollow spots!
2. How was the heating mat of the "floor heating" embedded? Hopefully not with tile adhesive, right?
Regards Medic